Embodiments of the invention generally relate to regenerative thermodynamic cycles, e.g., regenerative Brayton cycles, and more particularly to power generation systems e.g., gas turbine power plants, leveraging the regenerative Brayton cycles and methods for operating the systems.
Regenerative thermodynamic cycles are typically implemented to gas turbines and micro-turbines to improve the cycle (e.g., Brayton cycle) efficiency beyond what is otherwise achievable with a simple cycle machine. In current regenerative gas turbine cycles, a partial replacement of the fuel energy is achieved by regeneratively transferring energy from the exhaust gases via heat exchangers to the air discharging from the compressor. The compression ratio in such a machine is low enough that the temperature of the exhaust gas leaving the turbine and entering the regenerator is higher than the compressor discharge air to be heated therein. A substantial improvement in the efficiency of the gas turbine cycle has been realized.
Further improvements to these gas turbine cycles have been achieved by using various processes and configurations, for example, multistage compression with intercooling, multistage expansion with reheating, and recompression. However, even in such recuperated and recompression cycles, the thermal efficiency is limited by the fact that the temperature of the turbine exhaust gas can never be reduced below that of the compressor discharge air, or else the heat will flow in a reverse direction (to the exhaust gases), decreasing the efficiency of the system.
More recently, there has been an increased interest in using supercritical fluids, such as supercritical carbon dioxide, in closed thermodynamic power generation cycles. For example, a supercritical Brayton cycle power generation system offers a promising approach for achieving a higher efficiency and more cost-effective power conversion when compared to the existing steam-driven power plants and gas turbine power plants. However, the turbomachinery designs for such a power generation system are complex and challenging mainly because of (i) a large number of components required/used in the system, and (ii) the high fluid density of the supercritical fluid. In particular, it may be challenging to match the fluid flow and the speed of the expander and the compressor such that the mechanical design is optimized to minimize stresses and the net axial thrust loads, and also to ensure controllable operation at off-design conditions.
Therefore, alternative configurations for the regenerative thermodynamic cycles are desirable, which provide advantages over conventional thermodynamic power generation cycles, typically, used in the power generation systems.